The invention relates to a piston for an internal combustion engine.
A piston for internal combustion engines is known from EP 0 902 180 A2. In this piston, the bosses are set back in the axial direction of the piston-pin bolt such that the outer boss measurement is 60 to 65% or less of the piston diameter. The boss outer surfaces which interconnect the two running surfaces have a straight (linear) shape when viewed over the height of the running surfaces. In this piston the boss outer surfaces (also called box walls) are not categorically planar but also curved in cross-section both parallel as well as perpendicular to the piston axis. However, the direction of the curvature of the surface in cross-section perpendicular to the piston axis is always constant for the entire surface of the box wall. With the distance between the box walls diminishing in the upward direction (towards the piston head), the result is decreasing width for the load-bearing running surface in the upward direction. The disadvantage is that when the distance of the box walls from each other widens, the potential for weight savings by undercutting the ring zone in the direction of the piston-pin bore cannot be fully utilized. The support for the piston head provided by the box walls is not optimal because of the reduction in piston head tensile strength. When the distance of the box walls narrows in an upward direction (towards the piston head), skirt area which is needed to keep the piston straight and to provide protection against seizing is lost at the skirt upper edge. In addition, because of the lack of support for the ring zone, high stresses result in the transitional area between the piston skirt and the casting around the ring zone.
Connecting walls are also known in pistons which are configured as planes parallel to each other or curved surfaces with only one radius of curvature and only one direction of curvature.
A piston, such as is known from DE 101 45 589 A1, offers an improvement. Said piston has a free casting (undercut) in the piston head which extends radially and peripherally behind the ring zone. This free casting has the advantage of reducing weight but at the same time the disadvantage is that the vicinity of the piston head is weakened as a result.
It would be desirable to provide a piston which eliminates the disadvantages described.